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This comprehensive study examines the effect of particle size and atomic ordering on the intrinsic and hysteresis properties of FePt nanoparticles embedded in a carbon matrix formed by annealing sputtered FePt/C multilayer precursors. Structural studies show a transformation from the magnetically soft to the tetragonal FePt phase dependent on the annealing conditions. The magnetic properties scale as a function of particle size. The coercivity depends, in part, on the vol % of carbon and develops with annealing as a result of increased atomic ordering. Under the right conditions a high coercivity of 34 kOe has been achieved. Remanence curves show a variation of interparticles interactions from exchange to magnetostatic with increasing vol % carbon. Time dependent measurements indicate a decrease of the activation volume converging to the actual particle size ͑determined by TEM͒ as the carbon content is increased. The potential for future magnetic recording media is discussed.

In this study we present a technique to obtain ordered fct FePt particles embedded in a C matrix. FePt nanoparticles are formed inside a high-pressure sputtering cell, called a particle gun (PG), and subsequently deposited on the substrate through a small orifice. These particles have a uniform size distribution with an average particle size that can be controlled in the range of 3–10 nm by adjusting the sputtering cell pressure, power, distance between the magnetron and the orifice, and by using a liquid nitrogen cooling jacket. The particles are converted to the L10 phase as they pass through a specially designed heating stage, attached to the top of the PG, heated by halogen lamps, thus avoiding alloying and oxidation effects. A strong dependence of coercivity on both the particle size and temperature was observed.

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